The present invention relates to a hydraulic control system, particularly for an automobile vehicle brake device, comprising independent first and second brake circuits, and having a master cylinder including a first chamber in communication with the first brake circuit and whose pressure is controlled by movement of a master piston under the action of a brake pedal, while the second brake circuit is in communication with a second chamber whose pressure is dependent on that of the first chamber and is developed by a source of assisting hydraulic pressure under the control of a valve adjusted by the pressure of the first chamber.
The source of assisting hydraulic pressure is for example a positive displacement pump, and in this case the valve is in the form of a relief valve. The hydraulic pressure source may also be of the constant pressure type, and the valve is then in the form of a distributor.
A control system of the type indicated above combines the advantage of safety provided by the two independent circuits with that of easy, sensitive operation, because the master piston acts on one of the circuits and the assistance on the other.
In known systems of this general kind, the second chamber connected to the second circuit is in direct communication with the source of assisting hydraulic pressure. If the assistance should fail, for example because its pressure source is out of action, the second circuit will itself be out of action, and braking will be possible only by means of the first circuit under the action of the master piston.
The present invention has as its object to provide a hydraulic control system, particularly for an automobile vehicle brake device, in which failure of the assistance does not thereby entail the failure of the second circuit.